The present invention relates to a method and a device for recording ultrasonic images, specifically for real-time recording and displaying three-dimensional ultrasonic images, in accordance with the introductory clauses of claims 1 and 12, as well as to the application of this method or this device in accordance with the claims 17 to 19.
Such methods and devices for recording ultrasonic images of an object are known, wherein an ultrasonic emitter emits ultrasonic waves onto an object while an ultrasonic receiver receives the ultrasonic waves reflected by the object. For recording the object, the ultrasonic emitter or the ultrasonic receiver, respectively, is displaced along the object or rotated relative to the object while individual image sub-areas of the object are recorded. As a rule, these partial image areas correspond to a linewise scanning of the object, in which operation the object is recorded by lines along a recording direction in which the ultrasonic emitter or the ultrasonic receiver is displaced. In the known ultrasonic devices, the images generated in the ultrasonic device can be transferred in digital form or via a video output into a post-processing device or into a data processing system, respectively. There the images can be stored or directly post-processed.
With the scanning operation the object to be examined is recorded by lines, which means that individual xe2x80x9clayersxe2x80x9d of the object, which are parallel to each other, or xe2x80x9cslicesxe2x80x9d of the object, which are in mutual rotational symmetry, are exposed to ultrasonic waves and that the corresponding reflected ultrasonic waves are received in the ultrasonic device. The received ultrasonic waves are processed in the data processing system such that a halftone image is produced on a display device, with the individual halftones corresponding each to ultrasonic waves reflected more strongly or weakly.
The individual layers or slices of the object, i.e. the individual lines recorded in the ultrasonic scanning operation are xe2x80x9csuperimposedxe2x80x9d in the data processing system so as to obtain a three-dimensional representation of the object on the display device. The different spacings of various regions of a layer, i.e. the position of cavities or regions of more strongly compacted material of the object relative to the ultrasonic device, are obtained by evaluation of the halftone information of each layer.
A sound transmitting medium, which enhances the propagation of ultrasonic waves, is provided between the ultrasonic device and the object to be recorded. This sound transmitting medium is represented by a uniform halftone in the corresponding halftone image. In particular, the outside contours of an object can be determined by the provision that the first halftone variations on the boundary between the sound transmitting medium and the object to be examined are detected in the halftone image and that their respective relative spacing from the ultrasonic device is measured.
The ultrasonic methods make use of a pre-defined halftone grade (threshold) or a grade to be computed in order to find contours in the image. The contour information is then stored in an image and, after evaluation of the respective spacings between the ultrasonic device or the ultrasonic transmitter, respectively, and the outside contours of the object to be examined, furnish then a three-dimensional impression of the image.
These known ultrasonic methods are suitable, for instance, for examining a foetus inside the mother""s abdominal cavity or for detection of renal calculi inside the human body. For recording the object to be examined, which is located, for instance, inside the human body, the ultrasonic device is connected to the skin surface on the human body by means of a sound transmitting medium such as a gel, oil or waters and is then moved or rotated along a desired recording direction whilst ultrasound images are recorded during uniform distances in time or space. The entire scanning operation extends over a defined area of the human body, with individual layers or slices of the object under examination inside the body being recorded during the scanning operation in succession. The individual ultrasonic images are then joined in a spatially correct succession in a subsequently employed data processing system so that a complete or three-dimensional image of the object is achieved by xe2x80x9csuperimpositionxe2x80x9d of the individual images. Then xe2x80x9cartificialxe2x80x9d two-dimensional images in this three-dimensional image can be calculated in the data processing system.
Ultrasonic techniques employed in practical clinical applications for the three-dimensional recording of human organs are presently operating on a tomography basis, which means that the volume is composed of the individual recorded layer planes or slices. In trans-oesophageal echo cardiography, for example, a pivotable endoscopic probe is introduced through the patient""s oesophagus. The ultrasonic sensor is integrated as so-called xe2x80x9cphased arrayxe2x80x9d into the tip of the probe. In this technique the ultrasonic transducer on the tip of the probe is linearly shifted or rotated so that a layer of the organ is scanned from each angular position of the rotating ultrasonic transducer or from each shifted probe position. One image sequence, i.e. one or several cycles of movement of the organ, such as a cardiac cycle, is produced per layer.
When such a sequence has been recorded the rotation of the ultrasonic transducer is continued by a desired angular increment, using a motor such as a stepping or linear motor, or the transducer is shifted by hand or along a linear path in the case of linear shift. Then a data processing system triggers the next recording sequence, with this data processing system being capable of processing both the data of the electro cardiogram (ECG) and the respiratory or thorax movements (respiration scan).
With coupling the ECG to the recording times an attempt is made to record each image of a sequence always at a defined phase point during the cycle of the hear beat. As a result, it is possible to generate sequences of three-dimensional images of moved objects or organs inside organisms, which, when joined in succession, furnish a three-dimensional representation of the organ as a function of time. The organ movement can then be cyclically viewed as in a xe2x80x9cfilmxe2x80x9d.
It is particularly important in these methods that the distances between the individual xe2x80x9clayersxe2x80x9d, i.e. between the individual image sub-areas of the object under examination, are almost constant in order to avoid a longitudinal distortion of the overall image along the recording direction, i.e. along the scanning axis. In order to achieve a uniform recording rate, i.e. a uniform rate of the ultrasonic transducer along the recording direction during the scanning operation, the conventional techniques either operate on motor-controlled mechanical systems for moving the ultrasonic device or magnetic position detectors or optical systems for detecting the respective precise position of the ultrasonic device with respect to the corresponding record of the image sub-area, i.e. the corresponding xe2x80x9clayerxe2x80x9d of the object under examination. Due to the detection of the precise position of the ultrasonic device during the operation of recording such a xe2x80x9clayerxe2x80x9d it is possible later on to compose the individual image sub-areas, i.e. the individual xe2x80x9clayersxe2x80x9d of the object examined, in the data processing system in a form corresponding to reality. In the conventional systems image distortions along the recording direction can hence be avoided.
From the German Patent DE 38 29 603 A1, for example, an ultrasonic endoscopic device is known that is provided, over a distal terminal section, with a flexible hose accommodating a longitudinally displaceable ultrasonic transducer on a slide for the creation of multi-plane tomograms. In this case, too, a defined volume is to be scanned in multiple planes with high precision in order to be able to reconstruct a precise three-dimensional representation of the sectional images so obtained. There the slide is displaced by an associated Bowden cable operated by a motor along the distal terminal section for appropriately recording the individual layer images.
The U.S. Pat. No. 5,159,931 discloses a rotating ultrasonic probe which records individual slices in rotational symmetry of the organ under examination; there the probe is equally rotated by means of a motor that rotates the probe by increments in correspondence with a specified succession of increments so that the precise position is known for each recorded layer plane or each slice, respectively, so as to permit an assignment of the individual image sub-areas of the rotational images with each other in the data processing system.
These conventional systems present the disadvantages that the respective ultrasonic equipment is highly complex and very expensive to manufacture, that the recording method is very complicated to handle, and that the operator, i.e. the physician examining a heart, must expect very long recording and post-processing times.
The known motor-controlled recording systems equipped with motors, which record the respective organs both in parallel and by means of a so-called xe2x80x9csweepxe2x80x9d or by a rotation of the ultrasonic transducer, moreover require a permanent calibration of the respective motors, a motor controller, as well as the supply of energy up to the region of the organs in organisms inside which the motors are moved, which involves potential risks for the patient. Even the known systems provided with position sensors (cf., for instance, the German Patent DE 196 08 971 A1) require a complex expenditure in terms of apparatus as well as the calibration of the systems and possibly a so-called xe2x80x9cresetxe2x80x9d position in order to be able to determine the initial position of the ultrasonic transducer by the beginning of the ultrasonic recording cycle.
The present invention is now based on the problem of improving the methods and devices of the aforementioned general type in an approach to render motor-controlled mechanical systems or position detections of the ultrasonic transducer dispensable whilst a simple, low-cost ultrasonic method or ultrasonic device is proposed that is easy to handle.
The present invention solves the afore-defined problem by the features defined in the characterising clauses of claims 1 and 12. Expedient embodiments of the invention are characterised in the respective dependent claims; some applications of the inventive device or of the respective method are identified in the claims 16 and 17. In accordance with the present invention an object to be examined, that is located, for instance, in an inaccessible body or part of the body, is recorded by means of an ultrasonic device. There, the ultrasonic transducer, that contains expediently the ultrasonic emitter and the ultrasonic receiver, is moved, rotated or pivoted in a fan pattern along the recording direction whilst individual image sub-areas of the object, i.e. individual xe2x80x9clayersxe2x80x9d or slices of the object are recorded. These layers are stored in a data processing system and evaluated on the basis of the aforementioned halftone analysis. Then the layers are composed again with reference to the recorded succession so that a three-dimensional ultrasonic image of the object under examination will be obtained.
The resulting image may be displaced in two-dimensional or three-dimensional form; possibly a plurality of these two- or three-dimensional images may be joined in succession to produce moving images, so-called four-dimensional images. These images can also be marked in colours so as to achieve an impression of the object under examination that is easier for the operator to survey. In addition to this halftone information (B mode) it is also possible to detect the colour, movement or flow information (xe2x80x9ccolour flowxe2x80x9d) or any other additional video information in the same manner. With this technique several images are taken of one site of the moving object, with the respective images (a plurality of image sub-areas) of a condition of movement of the object being composed to form a respective resulting image. The plurality of resulting images in succession then furnishes a moving representation of the object (film projection).
To determine the precise succession of the individual layers or slices of the individual image sub-areas and for establishing, in particular, the respective distances between the individual layer planes, the movement of the ultrasonic emitter or the ultrasonic receiver, respectively, is detected in increments by means of a detector and then associated with the individual image sub-areas. The ultrasonic transducer when moved by hand, for instance by the physician, can be displaced or rotated along the object while an increment detector serves to sense the incremental detection of the movement.
The ultrasonic emitter or the ultrasonic receiver, respectively, is expediently displaced or rotated along the recording direction at a uniform speed so as to obtain sectional planes spaced from each other by approximately the same distance, even though this would actually not be necessary on account of the increment detector. The mutual spacings of the individual image sub-areas are determined by the analysis of the positions of the ultrasonic sensor or the ultrasonic receiver, respectively, which are detected by steps and which had previously been associated with the individual image sub-areas. When objects are recorded it is expedient, for instance, to displace or rotate the ultrasonic transducer at a uniform speed while the corresponding image sub-areas are either passed on via image data lines to a data processing system or buffered in the ultrasonic equipment. At the same time, the increment detector or the. detector, respectively, communicates the lengths of the individual steps in the movement or rotation of the ultrasonic transducer, which are then associated with the individual image sub-areas in correspondence with the time lapsed. In this operation it is also possible to attach the corresponding positions of the ultrasonic transducer, which are determined via the increment detector, together as so-called xe2x80x9cheadersxe2x80x9d to that data package that corresponds to an isolated image sub-area.
In particular, the number of the incrementally detected positions is approximately the same or even higher than the number of the recorded image sub-areas so that it will be ensured that at least one position of the ultrasonic transducer will be available for each image sub-area. With the recording of the individual image sub-areas and the detection of the positions by the increment detector mostly not being synchronised in this very plain system, the detection of a plurality of different positions is recommended so that the correspondingly precise position can be detected for each image sub-area and associated with the latter with a very high degree of approximation.
For recording moving objects such as a heart the states of motion or the absolute or relative time stamps (i.e. relative to an event such as the occurrence of the ECG R-peak) of a moving object are detected in addition to the images of the individual image sub-areas, whereupon the incrementally detected positions and the individual image sub-areas are associated with the states of motion of the object.
Subsequently, the incrementally detected positions and time stamps are associated with the images of the individual image sub-areas in the aforedescribed manner and then composed and displayed in correspondence with the states of motion of the object. With this technique the aforementioned xe2x80x9cfour-dimensionalxe2x80x9d images are achieved. Here the points of time for recording individual image sub-areas of the moving object are expediently controlled by the movements of the object as such. To this end signals of the electrocardiogram, the respiration, the movements of the stomach, the peristalsis of the oesophagus or a combination of these signals from the organism are employed for determining the points of time by which the individual image sub-areas are recorded. The ultrasonic emitter or the ultrasonic receiver, respectively, may be moved along linear, circular, bow-shaped or free-hand lines along the object, with appropriate increment detectors or detectors being applied in correspondence with the movement for incremental detection of the movement of the ultrasonic transducer. The individual regions of the object, which present different intensities in correspondence with the recorded halftone images and/or colour information, or differently moving areas of the object can be identified by colour markings in the display in order to facilitate the detection of the individual regions of the organ for the physician.
In this manner it is possible to process and/or display the images formed from the individual image sub-areas in real time while the object is recorded so that the physician can examine the organ manually for better observation of the progress during an operation, for example.
Mechanical, optical or electromagnetic motion sensors known from prior art already may be used as increment detectors for incremental detection of the movement. Examples are the systems known from a xe2x80x9ccomputer mousexe2x80x9d for detecting the mouse movements by means of optical sensors or spherical detectors determining the sensor movement in two dimensions. Moreover, rotationally symmetrical increment detectors are suitable to detect the linear movement of an ultrasonic transducer. When the ultrasonic transducer is freely moved in space correspondingly designed mechanical systems are suitable for the incremental detection of all degrees of freedom of the ultrasonic transducer. It is also particularly advantageous to integrate the increment detector into the ultrasonic transducer and to provide appropriate measuring detectors or transducers for the incremental detection of the movement of the ultrasonic transducer relative to its surroundings. This is possible, for instance, with spherical bodies on the outside shell of the ultrasonic transducer, which detect this relative movement by increments as the ultrasonic transducer is moved along a surface.
The inventive method or the inventive device, respectively, is particularly suitable for recording the heart of an organism in consideration of the movement of the heart for displaying a moving, specifically four-dimensional image. With this technique it is possible to record the organ of the organism or parts of this organ by means of an ultrasonic method with trans-thoracic, trans-oesophageal, abdominal, trans-rectal or trans-vaginal application, and moreover by intra-vascular or intra-ductal application when an ultrasonic catheter technique is employed. Furthermore free-hand recording with an ultrasonic transducer moved by the physician on the patient""s body surface or, with an intra-operative technique directly on or in the organ can be realised in a manner similar to the control of a computer xe2x80x9cmousexe2x80x9d.